qt3d sometimes fails to build on osx

compiling 5.7.0-rc (sometimes) fails with the following error when
building qt as static library:

> error 15-Jun-2016 20:04:06 make[4]: *** No rule to make target `/Volumes/build/bamboo-build/THIRDP-QT9-BUILDMAC/build-Qt-5.7.0-rc-macx-clang-static/qt3d/lib/libQt53DQuick_debug.a', needed by `../../../../qml/Qt3D/Extras/libquick3dextrasplugin_debug.a'. Stop.
> error 15-Jun-2016 20:04:06 make[3]: *** [debug-all] Error 2
> error 15-Jun-2016 20:04:06 make[2]: *** [sub-quick3d-imports-extras-make_first] Error 2

probably an missing dependency for parallel builds as it doesn't happen
all the time ...